Stream

[showbit01]

Hi,
I have signed the document and in the signature panel it's showing document has been altered or corrupted I have used the valid certificate how it could be ?
Any idea ?

[MatthiasValvekens]

There are many ways to screw up a signature ;). You won't get any actionable feedback if you don't share your code and explain what you are trying to achieve, at the very least.

[showbit01]

Apologize for the confusion.

1.I am writing field annotation to the input pdf stream and taking the updated stream as stream.pkl for signing:

Box = [(50,0,150,40),(500,0,350,80),(500,200,350,80)]

with open(input_pdf_path, 'rb') as inf:

w = IncrementalPdfFileWriter(inf, strict=False)


for i in range(3):

            Field_Name='Signature_2'+str(i)

            append_signature_field(Flag,
                w,
                SigFieldSpec(
                    sig_field_name=Field_Name,
                    field_mdp_spec=fields.FieldMDPSpec(fields.FieldMDPAction.ALL),

                    doc_mdp_update_value=fields.MDPPerm.FILL_FORMS,

                    # empty_field_appearance=True,
                    on_page=i,
             
                    box=Box[k]

                )
            )


buffer = io.BytesIO()

w.write(buffer)

x = byte_hash(buffer)
print(x)

with open('stream.pkl', 'wb') as file:
    pickle.dump(buffer, file)

2.After getting updated steam.pkl, i am signing pdf from this stream.

Box = [(50,0,150,40),(500,0,350,80),(500,200,350,80)]
with open('stream.pkl','rb') as file:
w= IncrementalPdfFileWriter(inf,strict=False)

timestamp = datetime.now()
md_algorithm = 'sha256'

for i in range(3):
    timestamp = datetime.now()

    data = base64.b64decode(coded_string)

    if i>0:
        w = IncrementalPdfFileWriter(output, strict=True)


  cms_writer = cms_embedder.PdfCMSEmbedder(Flag).write_cms(


        field_name=Field_Name, writer=w

    )
    sig_field_ref = next(cms_writer)


# #assert sig_field_ref.get_object()['/T'] == 'Signature'

    appearance=cms_embedder.SigAppearanceSetup(style= stamp.TextStampStyle(
                        stamp_text=' ',
                        # text_box_style=text.TextBoxStyle(
                        #     font=opentype.GlyphAccumulatorFactory('NotoSans-Regular.ttf')
                        # ),
                        background=images.PdfImage(img_path, opacity=1), border_width=0,
                        background_layout=layout.SimpleBoxLayoutRule(
                            x_align=AxisAlignment.ALIGN_MID,
                            y_align=AxisAlignment.ALIGN_MIN,
                            # margins=Margins(left=10, right=10, top=5, bottom=5),
                            )),
                        timestamp=timestamp,
                        name='',
                        )
    sig_obj = signers.SignatureObject(timestamp=timestamp, bytes_reserved=20440)



    cms_writer.send(
        cms_embedder.SigObjSetup(
            sig_placeholder=sig_obj,
            mdp_setup=cms_embedder.SigMDPSetup(
                md_algorithm=md_algorithm,
                certify=True,                
            
                docmdp_perms=fields.MDPPerm.FILL_FORMS,
                ),

                appearance_setup=appearance,
        )
    )

    prep_digest, output = cms_writer.send(
        cms_embedder.SigIOSetup(md_algorithm=md_algorithm, in_place=True)
    )

    hashb64 = base64.b64encode(prep_digest.document_digest).decode()

    der_bytes = data
    # if pem.detect(der_bytes):
    #     print(11)
    #     type_name, headers, der_bytes = pem.unarmor(der_bytes)
    # cert = x509.Certificate.load(der_bytes)

    sig_contents = cms_writer.send(der_bytes)



with open(output_pdf_path, "wb") as outfile:
    outfile.write(output.read())

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The signed pdf showing is corrupted or altered here the attached screenshot of signed pdf.